Text 609, 82 rader
Skriven 2009-10-17 18:21:24 av Roy Witt (1:387/22)
    Kommentar till text 600 av Robert Bashe (2:2448/44)
Ärende: Foundry work (was: Child labor)
=======================================
17 Oct 09 10:37, Robert Bashe wrote to Roy Witt:

 RB> Roy Witt wrote to mark lewis on Friday October 16 2009 at 11:13:

 ml>>> the main idea is to show that there is a mold that is created when
 ml>>> needed, metal is poured into it and after a bit of time, the engine
 ml>>> head or block or whatever is removed and final steps are done to it
 ml>>> (like grinding off flash and other wastage) before it is sent on to
 ml>>> the next station where it is mated with other parts and assembly
 ml>>> goes on...

 RW>> Before it gets that far, someone has to physically remove the resin
 RW>> sand cores. We used cheap (minimum wage earners) labor for that.

 RB> That's called "shakeout" and nowadays is done by mechanically
 RB> vibrating the castings to "shake out" the cores. If the cores were
 RB> properly made, the binder has been incinerated by the heat of the
 RB> molten metal and the sand can then be removed without difficulty.

It's called 'poke and shake'...the laborer uses a piece of metal rod to
break up the sand core, then shakes it out. None of that modern crap in
the foundry where I worked.

 RB> It's amusing that when I was first interviewed for a job in a foundry
 RB> chemicals company, the manager told me that the products they made
 RB> had to bond sand as strongly as possible - and after the casting
 RB> operation must essentially disappear. At first glance, I thought the
 RB> idea ridiculous. But only at first glance.

We knew there wasn't enough resin in the sand when it broke before it got
placed in the mold. Sometimes they broke coming out of the sand core mold.
Add more resin and try again.

 RW>> We also had a giant band saw to remove sprues (wastage [sic]) from
 RW>> the casting.

 RB> The [sic] is justified, since the sprues are re-melted and repoured.
 RB> They are _not_ "wastage".

Even the machining op chips were re-melted.

 RW>> Since we cast in brass, ours were permanent molds made of a special
 RW>> blend of brylium copper.

 RB> Surprising, since permanent molds are mostly made of steel. That was
 RB> possibly something made necessary by the adhesion properties of the
 RB> casting metal.

Molten brass will stick to steel and burn up the mold. Besides, the
release agent was applied by dipping the molds in a carbon/water mix. A
steel mold will crack from the constant high-temp quenching. Been there
and was I chastised for even thinking of making a poured brass mold
out of steel. The difference in price between steel and bryllium copper
was staggering.

 RW>> Of course, the resin sand core molds were made of a mild steel and
 RW>> lasted a lot longer than the molds for casting brass.

 RB> Molds or copes and drags? Sand molds use the latter, and since they
 RB> are basically only hollow forms to hold the bonded sand, they
 RB> naturally last indefinitely. True permanent molds don't, but are
 RB> naturally much more expensive.

Permanent molds don't use copes, or drags for that matter. Picture this;
we cast a 10" long, 3/4" brass hexigon with a hole thru it's length by
making a sand core that set in the mold. When the pour was made, we had
hollow hex stock. We even experimented with casting left hand threads, but
the heat was too much for it and the threads in the mold died after a
while. I think my biggest challange was to design a sand core that was
made in two pieces and fit in a permanent mold to cast a brass bathtub
faucet. It worked the first time out.

Best part was the machine that was used to make sand cores was imported
from Germany, as was the resin we used. That's because of the American
chemical engineer who spent 30 some years at a German foundry.


                R\%/itt

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